Abstract

We demonstrate a technique for frequency measurements of UV transitions with sub-MHz precision. The frequency is measured using a ring-cavity resonator whose length is calibrated against a reference laser locked to the $D_2$ line of $^{87}Rb$. We have used this to measure the 398.8 nm ${^1S}_0 \leftrightarrow {^1P}_1$ line of atomic Yb. We report isotope shifts of all the seven stable isotopes, including the rarest isotope $^{168}Yb$. We have been able to resolve the overlapping $^{173}Yb$($F = 3/2$) and $^{172}Yb$ transitions for the first time. We also obtain high-precision measurements of excited-state hyperfine structure in the odd isotopes, $^{171}Yb$ and $^{173}Yb$. The measurements resolve several discrepancies among earlier measurements.